It was Friday, the day after Carla stayed. I rang my girlfriend at lunchtime from my office.

"You ok?"

"Tired, need a good night's sleep."

"Reckon you'll get that with a sore arse? Inviting your boss to stay has implications."

"You did well out of it."

"That's as may be, my house, my rules. Be ready."

"Perhaps I'll ask Carla round."

"Then you can both get your arses walloped."

I got home at just after six. There were no extra cars there. I half expected to be jumped by a naked girlfriend as soon as I walked through the door. Instead, she was standing in the kitchen, black skirt, white polo neck, bare legs. I walked over and placed my hands around her waist from behind, kissing her neck as I did so. I moved my hands upwards; her breasts were loose under her top and her nipples were already standing proud.

"Waiting for me? You look nice; is that skirt new?"

"Look, I'm sorry about last night. I should have asked but Carla had a problem. It all worked out nicely, though." She smirked.

"Enjoy a bit of girl-on-girl, did you? Or was it seeing me with another woman? Bad girl."

"Yes, I need to be punished, don't I?"

I took her by the hand and led her upstairs. The curtains were drawn. Despite her protestations, my girlfriend liked to be spanked.

"Assume the position."

She stood at the end of the bed and leaned forward onto her elbows, raising her shapely arse in the air. "You will receive four sets of six. Two for inviting overnight guests without checking with me first, one for your debauched behaviour with another woman, and one for your voyeurism. You may speak, do you agree?"

"Yes."

"Each set of six will comprise three blows with my hand to your right cheek, then three to your left. After each set, I will pause. You will part your legs slightly. I may touch you. It is my choice. I may finger you, that is my choice. I will not fuck you. You will say nothing. You will not move in any way. If I suspect you are attempting to derive pleasure, then further sets will be added. You may speak, do you agree?"

"Yes."

"Once the punishment starts, if you wriggle, make a noise, attempt to protect yourself, or try to gain pleasure in any way then the set will be restarted. You may only speak to say the safety word, your name. I will now start." I lifted her skirt high onto her back. She stood with legs slightly parted, lips already glistening, and her perfect round buttocks elevated. "You are improperly dressed; only very bad girls do not wear knickers. You will receive an extra set." Thirty strokes, this would hurt her. It would also hurt my hand.

I ran the fingers of my right hand across her backside, down to the sit spot, where her bottom joined her leg. She tensed her muscles as I raised my hand. I made contact higher than I had intended. The loud "thwack" preceded the emergence of a red hand-shaped mark on her buttock. The second found its mark, and the third followed. I changed sides, observing the redness of one side of her arse. The fourth caught her square on the spot, nearly lifting her off her feet. The fifth was high, as was the sixth. The first set was over, and I paused.

She relaxed and moved her feet slightly. She was dripping wet. I waited, then gently stroked her lips with one finger. She held her breath but, to her credit, stayed still. As ever, the second and third sets were the most powerful as I warmed up and got my eye in. By the fourth set her arse was entirely red, it must have felt like it was on fire, especially when I inserted my finger two knuckles deep into her rosebud.

Despite running out of steam, I landed four out of six on the sit spot in the final set. She knew the rules, she stayed in place even once the last set was complete. "Your punishment is complete, please stay in position. Do you have anything to say?"

"Thank you, I will improve my behaviour in future."

"What would you like to happen now? It's lady's choice."

"I would like to be fucked in this position, please. I would like to be fucked hard in the pussy like the bad girl I am."

I fingered her swollen, wet pussy, getting that wonderful hot knife through butter sensation as I entered her. I added a second finger, and she gasped. I undid my belt and dropped my trousers and boxers. I was almost painfully hard, and I worked the tip up and down her dripping slit before driving into her, right up to the hilt. She yelped. I grabbed her hips and drove deeper, pushing my stomach against her red backside. She pushed back against me, and I started to pound her willing flesh from behind.

She was very turned on by the spanking and she came after barely half a dozen thrusts. By then my hands were under her shirt, latched onto her breasts. She squeezed me with her pussy muscles and screamed. I waited for her to relax then started pounding again, slower this time, bringing her to another peak. She tightened around me again, and then her insides seemed to go into spasm around me, as if they were milking my cock of its juices. She was shouting and screaming her head off as the pleasure overcame her. Then she clamped onto me, harder than I've ever known her before and I coated her insides just as she went over the edge.

We lay on the bed. She had her back to me, her backside pressed against me. I swear I could feel the heat coming from it. I cradled her tits.

"Bloody hell, that was good," she said. "Let's shower and go to the pub, I'll deal with whatever's pressing into my arse later."

"Remember your knickers this time."

She smirked at me, turned, and stuck her pert red arse towards me so I could admire my handiwork.